This is an old trick but worth repeating. Occasionally tubes that appear tohave open filaments really don't. The solder joint(s) at the pins can be cracked,have poor solder joints or the wire has enough corrosion to cause the connectionto be poor. The solution is melting the solder on each filament pin, removeold solder with a solder sucker then clean the wires and pins as much aspossible before applying new solder. I'll usually use a small amountof rosin to help the new solder adhere.

I've resurrected old and newer tubes this way. Today it was an Eimac 250Twhich is getting to be an expensive tube.

This doesn't work very often but its worth a try with octal and pre-octaltubes as well as larger tubes that have soldered pins. No, this won't workwith compactrons or 7 & 9 pin tubes. Steve

_________________'cell phones and the internet are tools, not a lifestyle'

The early tubes used a high tin solder. The tin develops a corrosion and the joint to the tube wire element breaks away. The high tin solder will be difficult to melt, so much so the additional heat can blister the Bakelite tube base. The trick is to file some of the tin off the end of the pin, add active rosin flux, then apply fresh solder, the fresh solder will amalgamate with the tin and allow easy extraction of all the tin and solder, lowered melting point. Using an Exacto knife with the pointed blade to scrape the inside of the pin and the sides of the element wire. applying a small amount of flux and re-solder. This technique is particularly useful for salvaging 226's because of the high current filament. Time has caught up to most of the multi-pin tubes too and re-soldering can salvage quite a few.

_________________First they ignore you, then they laugh at you, then they fight you, then you win."Gandhi"

Last edited by Chas on Oct Sat 29, 2016 3:25 pm, edited 1 time in total.

There is a procedure for broken filaments also. The success rate of welding a filament is very low in my experience but has extended the life of a few expensive tubes for me. You apply high voltage to the filament pins and tap the tube to try to make the broken ends touch. If all works well, the filament fuses on contact and continuity is restored. I use a charged capacitor as the voltage source since it will discharge immediately so it will not burn the filament out again. It's pretty much the same procedure I use to restore open audio transformers for my 20's battery sets. I have over a 50% success rate with my audio transformers so far.You have to use caution handling charged capacitors. If you mishandle them you can receive a severe shock. Use well insulated connectors and make sure you are not grounded. I have a rubber mat in front of my bench that I stand on while working.

_________________I'm not a hoarder, I'm a caretaker of scarce commodities

There is a procedure for broken filaments also. The success rate of welding a filament is very low in my experience but has extended the life of a few expensive tubes for me. You apply high voltage to the filament pins and tap the tube to try to make the broken ends touch. If all works well, the filament fuses on contact and continuity is restored. I use a charged capacitor as the voltage source since it will discharge immediately so it will not burn the filament out again. It's pretty much the same procedure I use to restore open audio transformers for my 20's battery sets. I have over a 50% success rate with my audio transformers so far.You have to use caution handling charged capacitors. If you mishandle them you can receive a severe shock. Use well insulated connectors and make sure you are not grounded. I have a rubber mat in front of my bench that I stand on while working.

When using a charged HV cap to attempt to internally weld open windings inaudio transformers you MUST limit the current with an internal resistor or you'llcause more faults. In my case I use an old TV transformer that puts out about500 VAC, use a 10 K, 20 watt resistor in series and monitor the primarycurrent while slowly bringing it up with a variac. This usually doesn't workbut nothing to loose and I have been able to save some fairly rare 1920'sinterstage audio transformers this way. Steve

_________________'cell phones and the internet are tools, not a lifestyle'

O.T. No audio transformer is actually saved by creating a noisy carbon path within the windings. Winding resistance will go up, the arc path is not a valid resistor and prone to degradation for acid contamination and noise. I have done the forensics on such "repaired" transformers after getting "smoked" by a seller on a supposed "good" audio transformer. Copper expands by a factor of 67,000 times when it turns from a solid to a vapor.

_________________First they ignore you, then they laugh at you, then they fight you, then you win."Gandhi"

O.T. No audio transformer is actually saved by creating a noisy carbon path within the windings. Winding resistance will go up, the arc path is not a valid resistor and prone to degradation for acid contamination and noise. I have done the forensics on such "repaired" transformers after getting "smoked" by a seller on a supposed "good" audio transformer. Copper expands by a factor of 67,000 times when it turns from a solid to a vapor.

Sometimes the open winding will weld to an adjacent wire. Like I said thisdoesn't work very often but I have had some success. Its a last resort. Steve

_________________'cell phones and the internet are tools, not a lifestyle'

In 1969, we experimented with "fixing" picture tubes (CRT) for Rauland. I was working for Westinghouse and involved with ruby rod lasers.

Rauland had problems with electrode welds that had gone "open" in the neck area. We succeeded in shooting a laser through the glass and re-welding wires that were sufficiently close together.

Problem: the welding vaporized metal that migrated... guess where? On to the CRT phosphor and changed all the colors!

In a receiving tube, you might get lucky with an HV weld and the vapor will just condense on the glass, harmlessly.

Rich

I remember seeing a TV commercial on the old CBS series The 21st Century in which they showed a wire within a tube envelope being repaired by laser. I remember Union Carbide did many of the commercials for the show, But I'm not sure.

Tubes such as 5U4's etc. often have a heater current of 2 amps or more which can be troublesome for those dipped solder connections on the pins. Back in the 60's a parts salesman gave me a couple of "pin crimpers" made by the Berns company. You insert the heater pin of an octal tube and push down on the handle and it securely crimps the internal wire to the socket pin. This crimping slightly enlarges the tube pin so that it fits more securely in its socket.I have crimped many tube heater pins over the years using this tool. "Berns PT-1 & PT-2)"

Tubes such as 5U4's etc. often have a heater current of 2 amps or more which can be troublesome for those dipped solder connections on the pins. Back in the 60's a parts salesman gave me a couple of "pin crimpers" made by the Berns company. You insert the heater pin of an octal tube and push down on the handle and it securely crimps the internal wire to the socket pin. This crimping slightly enlarges the tube pin so that it fits more securely in its socket.I have crimped many tube heater pins over the years using this tool. "Berns PT-1 & PT-2)"

The Berns pin crimp tools originally came in 5 sizes. I have looked for decades and even run WTB ads here for the other sizes. I found one for the CRT pins/octal pins, but still looking & hoping to find the full set before I die. I crimp the pin, then run solder into it. Works like a champ!

_________________FrankBWB7ELC"The average family has 2.5 children. Where is the other .5 child?"

I have attached pix of the two crimpers I have from a clean-out of an old radio-TV shop. I wondered for years as to their function and kept them in an odd parts box. Thank you for opening this phase of the discussion. I can now put these devices to use should the need arise.

Attachments:

P1120569.JPG [ 91.22 KiB | Viewed 5256 times ]

_________________I'm not a hoarder, I'm a caretaker of scarce commodities

I know this is an old post, but I stumbled into it looking for ways to fix the filament on my old scope...

Anyway, had somebody thought of posting the construction or anatomy or plans of that much sought after BERNS PT-1 or PT-2 tool.A handy mechanical guy with the proper tools might be able to reproduce, and maybe even improve on that one.

It would be nice if people who owns it can give some construction detail, or detailed pictures, all kinds of cameras, even smart phone cameras are widely available these days!